What are secondary cataracts?
"Secondary cataract" is a phrase that is sometimes used to describe the slow blurring of vision after a cataract /lens implant procedure, usually after many months or years. I imagine the phrase was developed because the visual changes (hazy vision and loss of contrast sensitivity) tend to mimic the effects of cataract formation on vision. However, the term most eye doctors use is "Posterior Capsule Opacification" (PCO) although the cloudiness is rarely allowed to proceed to the point of actual opacification.
The hazy effect on vision that we call "secondary cataract" (or PCO) is from the slow fibrosis (scar tissue) and shrinkage of the "capsule" that surrounds the intraocular lens implant (IOL), sticking to it, and holding it in place. This capsule used to hold the cloudy natural lens. [That is actually what a cataract is -not a "film" or "covering" of the natural lens.] The capsule is not rigid like the name suggests -it is an elastic, transparent "shrink wrap" around the natural lens material attached 360º to the circle of muscle around it. By creating a hole in the front part of this capsule large enough to break up the lens material and remove it, the eye surgeon doing a cataract operation leaves the clear "envelope" of capsule that serves as the supporting structure for the new lens implant. But this cellophane-like capsule clouds with time, including the part behind the IOL. This is PCO or "secondary cataract." The solution is to open the cloudy capsule with a YAG laser. This creates a pupil-size opening in the posterior capsule (behind the IOL) for clear focus again while still leaving the peripheral, fibrotic capsule in the periphery to continue holding the IOL in place. It is extremely unlikely that this ever needs to be done more than the one time.
Trevor Woodhams, M.D., Chief of Surgery, Woodhams Eye Clinic